A new method for instantaneous quantification of leg muscle fatigue during cycle ergometry (LB797)

Abstract

Quantifying skeletal muscle fatigue (MF) during whole‐body exercise is confounded by the power‐velocity relationship. We reasoned that the relationship between isokinetic power and electromyography (EMG) would be linear, allowing MF to be quantified by deviation from this line. Using a rapid switch from standard (hyperbolic) to isokinetic cycling, we hypothesized that the EMG‐power relationship is: 1) linear and velocity dependent; 2) reproducible; and 3) sufficiently precise to quantify leg MF during exercise. Ten subjects (4 healthy and 6 COPD, GOLD 2/3, 29‐86 yr) repeated 5 s of isokinetic cycling at 50, 70 and 100 rpm from low to maximum effort, to determine baseline right‐leg EMG (of 5 muscles) and power (from crank torque and velocity). The patients also completed incremental exercise to the limit of tolerance, terminated with a maximal 5 s isokinetic effort to quantify MF. The EMG‐power relationship was linear (r² = 0.96±0.03), velocity dependent (p < .01) and reproducible (p > .05; ANCOVA). Mean precision (SEE) was 14±6 W. In COPD, isokinetic power was reduced from 167±64 W to 93±52 W at the limit of tolerance (p < .05) with MF contributing between 8 W and 50 W of the total. Establishing an individual’s isokinetic EMG‐power relationship is a reliable addition to a cardiopulmonary exercise test. EMG, combined with instantaneous hyperbolic‐to‐isokinetic switching ergometry, can quantify leg MF during exercise.Grant Funding Source: Supported by the Pulmonary Education and Research Foundation